The present invention relates to a security communication system and, more particularly, a communication system which can keep the communication secret from eavesdroppers with the same kind communication apparatus.
Generally, in communication systems except radio broadcasting systems or the like, it is desirable that communication is performed only between or among related parties. Particularly, in communications in which monitoring of a third party is undesirable, such as for example those by police radios and those including top secrets of nations, keeping the communications secret is very a important matter. Nevertheless, conventional communication systems of this kind permit third parties other than related persons to relatively easily monitor the communication. Diverse means to avoid such monitoring by unrelated persons have been developed and practiced; however, none of them have satisfactorily succeeded. Enhancement of the security of the communication needed a complex communication method. This results in complex circuits with a large number of parts, being accompanied by large size and high cost.